Yanfeng Xue

Pressure-induced crystallization of amorphous SiO2 with silicon–hydroxy group and the quick synthesis of coesite under lower temperature

The crystallization of amorphous SiO2 powder with free water and silicon–hydroxy group (Si-OH) was investigated in the range of 0–4.2 GPa and 150–1200 °C. The samples were detected by X-ray diffraction, transmission electron microscopy, thermogravimetry and differential thermal analysis, Raman and Fourier transform-infrared spectroscopy. The results show that amorphous SiO2 can transform to cristobalite at 1000 °C under room pressure. Under high pressure, amorphous SiO2 can quickly transform into single-phase coesite at lower temperature, and the P–T boundary of the crystallization products of mat1 (α-quartz and coesite) has been successfully obtained. Through comparing the crystallization products from amorphous SiO2 materials with the same grain size containing different forms of water under high pressure and high temperature, it is found for the first time that the synthesis of coesite can be quickened by virtue of Si–OH in the amorphous SiO2 at lower temperature. The single-phase coesite has been synthesized from amorphous SiO2 with Si-OH under 4.2 GPa and 190 °C for 30 min, and 190 °C is the lowest synthesis temperature of coesite so far.